The present invention relates to a magnetic recording write and/or read head, and more particularly to a magnetic head including a magnetic core in which two magnetic substances face each other through a working gap at a head section confronting a magnetic recording medium and at least one of the magnetic substances has magnetic anisotropy.
Today, a highly-developed magnetic recording technique, specifically, high-density magnetic recording is strongly demanded. In order to satisfy this demand, it is required not only to develop a magnetic recording medium having a high coercive force, a large output and low voise, but also to improve the recording characteristic and reproducing sensitivity of a magnetic head in a marked degree. Specifically, with an increase in recording density, the width of recording track is narrowed, and recently it is required to employ a recording track having a width of 20 .mu.m or less. In this case, when the core of a magnetic head is made of, for example, ferrite, the characteristic of the magnetic head varies widely, since the size of crystal grains forming ordinary polycrystalline ferrite is as large as the width of recording track. In order to reduce variations in the above-mentioned characteristic, the magnetic head is made of monocrystalline ferrite or oriented polycrystalline ferrite. The monocrystalline ferrite has the following advantages: (1) for high-accuracy finishing can be performed; (2) the wear rate of the surface of the magnetic head confronting to the recording medium is uniform; and (3) grain falling-off troubles never take place. Therefore, the magnetic head made of monocrystalline ferrite has been widely employed. However, there is no clear guiding thought as to how the crystallographic axis of the ferrite is to be oriented in the magnetic head. In usual, a favorable orientation of the crystallographic axis is selected in accordance with the manufacturing process of respective types of magnetic heads.
The present inventors have made a wider and deeper study as to how the crystallographic axis of a magnetic material is to be oriented to obtain an excellent recording/reproducing characteristic when a magnetic head is made of a magnetic material having magnetic anisotropy such as monocrystalline ferrite or oriented polycrystalline ferrite. The present invention is based upon the inventors' discovery that a high-performance head is obtained when an angle between that surface of the magnetic head which confronts a magnetic recording medium, and a direction having a maximum magnetic permeability in that part of a magnetic substance having magnetic anisotropy which is near a working gap, is made larger than an orientation angle of the above direction for minimizing the magnetic reluctance along a main magnetic circuit of a magnetic core by an angle within a specified range of angles.
In a magnetic substance having magnetic anisotropy, magnetic permeability varies with direction. That is, in the magnetic substance are two kinds of directions, one of which have a maximum magnetic permeability, and the other have a minimum magnetic permeability. For example, when a disc whose upper and lower surfaces are parallel to a crystal plane &lt;110&gt; is cut out of a ferrite single crystal having a positive magnetocrystalline anisotropy constant K.sub.1, the strain induced by working is removed, and magnetic permeability is measured in various directions in the above-mentioned plane, it will be found that the direction having a maximum magnetic permeability and the direction having a minimum magnetic permeability are directions &lt;100&gt; and &lt;110&gt;, respectively, in a relatively low frequency range. This relation is reversed in a high frequency range. Further, the magnetostrictive constants .lambda..sub.100 and .lambda..sub.111 of ordinary high-permeability Mn--Zn ferrite are given by the following formulae: EQU .lambda..sub.100 .ltoreq.0, .lambda..sub.111 .gtoreq.0
In the case where a tension having a large strength is applied to the upper and lower surfaces of the above-mentioned disc made of the Mn--Zn ferrite, the direction having a maximum magnetic permeability and the direction having a minimum magnetic permeability are directions &lt;110&gt; and &lt;100&gt;, respectively, in low frequency range, independently of the polarity of the magnetocrystalline anisotropy constant K.sub.1. This relation is reversed in a high frequency range. A frequency, at which the above-mentioned relation is reversed, varies depending upon the strength of tension, the value of magnetostrictive constant and the degree of magnetic anisotropy, and can be set within a range from 2 to 10 MHz.
It is well known that the characteristic of a magnetic head depends upon the shape of its magnetic core. As exemplified in FIG. 1, the magnetic core is so designed that a magnetic circuit is narrowed in the neighborhood of a working gap 11 in order to obtain a high efficiency. Incidentally, in FIG. 1, reference numerals 15 and 15' designate high-permeability magnetic materials, 10 a nonmagnetic filler for protecting a gap portion such as glass, and 1 a through hole for forming a ring-shaped magnetic circuit. In a wire-wound type magnetic head, a wire passes through the hole 1 to form a coil. The performance of a magnetic head having such a core as shown in FIG. 1 is mainly determined by the structure and the magnetic characteristic of the core in the neighborhood of the gap. Accordingly, when a magnetic core having such a structure is made of a magnetic material having magnetic anisotropy, it is a very important problem how the direction having a maximum magnetic permeability is oriented in the neighborhood of the gap to obtain a high-performance magnetic head.
In the case where a working gap is made in a bulk magnetic material such as ferrite, a magnetic substance 25 having a surface 23 confronting a recording medium and a slant 24 is attached through a nonmagnetic layer 22 to another magnetic substance 25' having a surface 23' confronting the recording medium and a slant 24', as shown in FIG. 2. Alternatively, as shown in FIG. 3, a magnetic substance 35 with a slant 34 is fixed through a nonmagnetic layer 32 to another magnetic substance 35' without a slant. Further, in the case where a magnetic head having a narrow track width is formed, the thickness of the core is made small only in the neighborhood of the gap and is made large in the remaining region in order to prevent the magnetic reluctance of a main magnetic circuit from being increased. In this case, a part of the core material is cut out in the neighborhood of the gap, as shown in FIG. 1, or grooves 46 are bored through the core material as shown in FIG. 4. Alternatively, a magnetic block 55 having a large width is attached to another magnetic block 55' having a small width and provided with a groove 50, as shown in FIG. 5. Further, as shown in side views of FIGS. 6A and 6B, a narrow portion 66a or 66b may be provided only on one side of a gap 61a or 61b. The performance of a magnetic head having such structures is determined by the characteristic of a track width defining part which forms the gap portion.
The following references are cited to show the state of the art; (i) Japanese Patent Appln. Post-Exam. Bubln. No. 10027/1968 (Japanese publication), and (ii) Japanese Patent Appln. Post-Exam. Publn. No. 10028/1968 (Japanese publication).